We have investigated the regulation of genes of proteins typically present in astrocytes or neurons. Glutamine synthetase (GS) mRNA is made in rats as early as E14 and then increases together with corticosteroids production. The GAP-43 protein typically found in nerve growth cones apparently is exposed to the neuronal cell surface because it can be labelled with iodine, is found to a small extent in astrocytes, and may be involved in astrocyte-neuron interaction. Certainly involved in this interaction is the protein laminin which is excreted into the extracellular matrix of astrocytes and serves as a neurite outgrowth factor for both PC12 cells and primary cerebellar and cortical neurons. The glial fibrillary acidic protein (GFAP) can be induced in certain cells by guanine deprivation. The genomic DNAs of GS, GFAP and the S- 100 protein are being isolated and the promoter region will be attached to a reporter gene in order to understand the induction of these proteins and the reason why they are specifically expressed in astrocytes. The five mRNA's of the muscarinic acetylcholine receptor (ml-m5) have been individually transferred to A1-L cells where only one receptor at a time is expressed. This has enabled the analysis of the coupling of the receptor protein to different G-factors, the sensitivity to pertussis toxin, the production of phosphoinositides or cAMP, and other properties. To complement other work in the laboratory, attempts are underway to isolate the genes involved with one of the glutamate receptors.